1. Field
The present invention relates generally to the construction of miniature modular electronic circuits and more particularly to miniature modular RF components, such as mixers, couplers, transformers, power splitters and the like.
2. Prior Art
For many years, surface mount electronic modular circuits have been constructed using a PC board to support the circuitry within the module. A case is placed over the PC board to protect the circuitry on the board of the case. The case also provides a flat surface for pick up by automatic assembly equipment.
FIG. 1 shows a bottom view of a prior art modular circuit with a case 1, a primary PC board 2, and terminals 3 connected electrically to the board. The terminals provide a means of external connections for this module.
FIG. 2 shows a front sectional view of the prior art modular circuit shown in FIG. 1. The sectional view permits viewing inside the module where internal components, such as a core 4, can be seen mounted on the PC board.
This type of prior art construction has eight principal disadvantages:
1. Assembled PC boards carrying components must be placed into the case and attached to the cover. The construction is costly because a PC board is required and the board with the components loaded on to it must be placed into the case and soldered to the terminals.
2. Once the board is assembled inside the case, it forms a semi-sealed area about the components which can allow water or other liquids used for cleaning the assemblies to become trapped in this area and to remain for long periods before they evaporate. Prior to evaporation these liquids can adversely affect the electrical performance of the module.
3. Leads from components which are to be connected to a terminal must follow a long lead path includes first being connected to a PC board land and then following a PC board trace to the terminal. This circuitous path add lead inductance which further detracts from the RF performance.
4. The presence of the PC board adds height to the module which is often unacceptable in modern miniaturized equipment, such as hand held cellular units.
5. The board first must be tested before it is placed within the case and then retested after it has been installed in the case. This requires running the same tests twice for the same component before it is acceptable for shipment.
6. Reduced reliability results from the added solder connections on the leads from the components to PC board traces and then on the leads from the traces to the terminals.
7. The prior art assembly system which using a primary printed circuit board results in less flexibility in the wiring because every component is typically tied to the primary printed circuit board. Wiring in a three dimensional manner is not possible. For example, a diode quad may have terminals on the top of its package which could be advantageously connected directly to another components or a terminal above the diode quad, if three dimensional connections were possible; however, with conventional circuitry using a printed circuit board, the diode quad leads must be first brought down and connected to the printed circuit board.
8. Conformal coating, which is required to withstand high voltage, is difficult to apply or inspect.
As electronic equipment becomes more complex, there is continuing industry pressure to improve the reliability while at the same time reducing the number of components and overall size of electronic module. There is also pressure to reduce the cost of assembly, components and testing. All of these industry objectives are met with the present invention.